bergson's philosophy op the organism. 19 



nitrifying bacteria which do essentially all that the green 

 plant does in the absence of light. Where, then, do 

 these organisms obtain the energy necessary for this 

 transformation? In attempting to answer this question, 

 we return to the consideration of the waste or unavailable 

 energy which is the product of all physico-chemical 

 processes. This energy exists in the form of low- 

 temperature heat, that is, in the motion of the individual 

 molecules of the substance into which unavailable 

 energy passes. When the mechanistic physiologist 

 speaks of this molecular motion, it is the mean motion 

 of all the molecules of which he speaks : he adopts the 

 statistical concept of molecular movement handled by the 

 mathematical physicist, but unlike the latter does not 

 note that the study of the individual molecules is also a 

 legitimate subject for enquiry. Yet he is far more 

 familiar than the physicist with the phenomena of 

 Brownian movements ; and the treatment of the individual 

 rather than a statistical mean of individuals is also more 

 familiar to him than to the physicist. Is it not strange, 

 then, that the enormous significance of the Brownian 

 movements should have been suggested by the physicists 

 and not (to my knowledge) by the physiologists? 



In a liquid containing particles exhibiting Brownian 

 motion what we observe is the motion of the particles 

 under the impacts of the molecules of the liquid. These 

 molecules are moving at greatly unequal velocities and 

 when the particle is small it continually happens that 

 groups of molecules hitting it on one side have altogether 

 greater momentum than those which hit it on the other 

 side, with the result that it is pushed in the direction in 

 which the molecules of greatest kinetic energy are 

 travelling. 



Are there organisms small enough to be affected by 



